Method and apparatus for improving quality of composite video signal and method and apparatus for removing artifact of composite video signal

ABSTRACT

A method of improving picture quality in a composite video burst signal includes dividing the composite video burst signal into a plurality of frequency bands using a low pass filter and a high pass filter, performing wavelet packet filtering of frequency bands including a chrominance signal having energy higher than a specified threshold among the plurality of frequency bands, and performing Wiener filtering of frequency bands including a chrominance signal having energy lower than a specified threshold.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority to Korean Patent Application No.10-2006-0052873, filed on Jun. 13, 2006, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods and apparatuses consistent with the present invention relate toimproving picture quality in a composite video burst signal, andremoving artifacts in a composite video burst signal.

2. Description of the Related Art

In a process of encoding video information in a National TelevisionSystem Committee (NTSC) system, a signal is encoded such that aluminance signal is modulated onto the low frequency part of the signal,and a chrominance signal is modulated onto the high frequency part ofthe signal. This signal is called a composite video burst signal (CVBS),and through a transmission and reception process, white Gaussian noise(WGN) is added to this signal. When the noise is thus added to thecomposite video burst signal, both the luminance and chrominance signalsare affected. Accordingly, noise having a variety of colors as well asnoise having black and white colors appears, and the picture qualitydeteriorates. In order to reduce degradation of the picture quality,much research has been carried out.

FIG. 1 is a block diagram illustrating a related art apparatus forimproving picture quality.

Referring to FIG. 1, in the related art apparatus for improving picturequality, if a composite video burst signal X_(CVBS) is input to adecoder 102, the decoder 102 separates the composite video burst signalX_(CVBS) into a luminance signal and a chrominance signal. The decoder102 extends the one-dimensional (1D) signal to a two-dimensional (2D) orthree-dimensional (3D) signal by applying a line delay and a framedelay, and filters the signal through a filter included in the decoder102. An artifact detection and removal unit 104 performs filtering ofthe signal X_(RGB) decoded by the decoder 102, and outputs anartifact-free signal X′_(RGB).

In the related art apparatus for improving picture quality describedabove, it is assumed that the noise in the video signal X_(RGB) afterthe decoding is white Gaussian noise. Furthermore, it is assumed thatthe noise is in a luminance signal, which has the most information inthe video signal, and thus removal of noise is performed in relation toonly the luminance signal. However, in the case of actual noiseoccurring in the process of transmitting and receiving a televisionsignal, noise is added in the process of transforming signals into acomposite video burst signal, and thus, noise having a color componentis generated in addition to the luminance signal noise.

Accordingly, after a composite video burst signal including noise isdecoded, if noise in a video signal X_(RGB) is analyzed, it can be seenthat the noise is composed of dots having black-and-white components anda variety of colors. Also, it can be seen that the pattern of the noisein the composite video burst signal is different from that of 2D whiteGaussian noise, which is used in the related art apparatus. Thecharacteristic of the white Gaussian noise changes according to adecoder used in the process of decoding, and thus, the noise becomes acolor noise form on a video plane.

The related art apparatus for improving picture quality cannot apply anappropriate algorithm to this noise, and thus, the improvement ofpicture quality by the related art apparatus is not effective.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention overcome the abovedisadvantages and other disadvantages not described above. Also, thepresent invention is not required to overcome the disadvantagesdescribed above, and an exemplary embodiment of the present inventionmay not overcome any of the problems described above.

The present invention provides a method and apparatus for improvingpicture quality in a composite video burst signal, and a method andapparatus for removing artifacts in a composite video burst signal, inwhich a filter is disposed before decoding is performed, and throughpreprocessing, noise in a 1-dimensional signal is removed and by using avariety of artifact detection and removal methods, picture quality isimproved.

According to an aspect of the present invention, there is provided amethod of improving picture quality in a composite video burst signalincluding dividing the composite video burst signal into a plurality offrequency bands by using a low pass filter and a high pass filter,performing wavelet packet filtering of bands including a chrominancesignal higher than a specified threshold among the divided plurality offrequency bands, and performing Wiener filtering of bands including achrominance signal lower than a specified threshold.

The performing of the wavelet packet filtering may include dividing thecomposite video burst signal further into a plurality of bands,generating wavelet transform coefficients by applying wavelet transformsto the plurality of further divided band signals, and removing a signalin a frequency band having a generated wavelet transform coefficientwhose absolute value is less than a specified threshold.

In the performing of the Wiener filtering, the size of a mask may bevaried with respect to the magnitude of a noise ratio.

The method may further include separating the filtered composite videoburst signal into a luminance signal and a chrominance signal,separating the chrominance signal into an in-phase signal and anorthogonal-phase signal, and transforming the luminance signal, thein-phase signal and the orthogonal-phase signal into an R signal, a Gsignal, and a B signal, respectively, in RGB space, and outputting anoutput video signal.

The method may further include detecting and removing an artifact of theoutput video signal, wherein the detecting and removing of the artifactincludes encoding the output video signal and outputting a predictedvalue of a composite video burst signal, and filtering the outputpredicted value of the composite video burst signal by using a YCseparation filter of a type different from that of a YC separationfilter for separating a luminance signal and a chrominance signal in asystem decoder.

The method may further include detecting and removing an artifact of theoutput video signal, wherein the detecting and removing the artifactincludes transforming the output video signal into a luminance signal,an in-phase signal and an orthogonal-phase signal, synthesizing thein-phase signal and the orthogonal signal into a chrominance signal,synthesizing the luminance signal and the synthesized chrominance signalinto a composite video burst signal, generating an artifact detectionmap indicating an area where an artifact occurs, by comparing theluminance signal and a signal obtained by low pass filtering thecomposite video burst signal, and filtering the area where the artifactis detected according to the artifact detection map by using a YCseparation filter of a type different from that of a YC separationfilter for separating a luminance signal and a chrominance signal in asystem decoder.

The method may further include detecting and removing an artifact of theoutput video signal, wherein the detecting and removing the artifactincludes estimates a motion vector from two neighboring frames in theoutput video signal, generates a motion detection map indicating whethermotion exists between two neighboring frames and a motion compensationmap indicating whether a motion compensation filter is used based on themotion vector, detecting a dot crawl artifact that is a dot crawloccurring in the vicinity of an outline of an image and generating a dotcrawl artifact map, or detecting a rainbow effect in which rainbowcolors are seen in an area where a big difference of brightness occurswhen an image moves fast, and generating a rainbow effect detection map,compensating for a motion according to the motion compensation map, andfiltering the area where the artifact occurs by combining a time filterand a space filter based on control signals of the motion detection map,the motion compensation map, the dot crawl artifact detection map in acurrent frame, the dot crawl artifact detection map in the previousframe, and the rainbow effect detection map.

According to another aspect of the present invention, there is provideda method of detecting and removing an artifact in a composite videoburst signal, including encoding an output video signal and outputting apredicted value of a composite video burst signal, and filtering theoutput predicted value of the composite video burst signal by using a YCseparation filter of a type different from that of a YC separationfilter for separating a luminance signal and a chrominance signal in asystem decoder.

According to another aspect of the present invention, there is provideda method of detecting and removing an artifact in a composite videoburst signal, including transforming an output video signal into aluminance signal, an in-phase signal and an orthogonal-phase signal,synthesizing the in-phase signal and the orthogonal signal into achrominance signal, synthesizing the luminance signal and thesynthesized chrominance signal into a composite video burst signal,generating an artifact detection map indicating an area where anartifact occurs, by comparing the luminance signal and a signal obtainedby low pass filtering the composite video burst signal, and filteringthe area where the artifact is detected according to the artifactdetection map, by using a YC separation filter of a type different fromthat of a YC separation filter for separating a luminance signal and achrominance signal in a system decoder.

According to another aspect of the present invention, there is providedmethod of detecting and removing an artifact in a composite video burstsignal, including estimates a motion vector from two neighboring framesin the output video signal, generates a motion detection map indicatingwhether motion exists between two neighboring frames and a motioncompensation map indicating whether a motion compensation filter is usedbased on the motion vector, detecting an artifact in which by detectinga dot crawl artifact that is a dot crawl occurring in the vicinity of anoutline of an image, a dot crawl artifact map is generated, or bydetecting a rainbow effect in which rainbow colors are seen in an areawhere a big difference of brightness occurs when an image moves fast, arainbow effect detection map is generated, compensating for a motionaccording to the motion compensation map, and filtering the area wherethe artifact occurs, by combining a time filter and a space filter basedon control signals of the motion detection map, the motion compensationmap, the dot crawl artifact detection map in a current frame, the dotcrawl artifact detection map in the previous frame, and the rainboweffect detection map.

According to another aspect of the present invention, there is providedan apparatus for improving picture quality in a composite video burstsignal including a preprocessing filter performing filtering of thecomposite video burst signal by using a wavelet packet filter and aWiener filter, a YC separation unit separating the filtered compositevideo burst signal into a luminance signal and a chrominance signal, acolor demodulation unit separating the chrominance signal into anin-phase signal and an orthogonal-phase signal, and a YIQ-RGB colorspace transform unit transforming the filtered luminance signal,in-phase signal and orthogonal-phase signal into an R signal, a Gsignal, and a B signal, respectively, in RGB space, and outputting anoutput video signal.

The apparatus may further include an artifact detection and removal unitdetecting which removes an artifact of the output video signal, whereinthe artifact detection and removal unit includes an encoder predictionunit encoding the output video signal and outputting a predicted valueof a composite video burst signal, and a decoder prediction unitdecoding the output predicted value of the composite video burst signaland outputting a predicted value of an input video signal.

The decoder prediction unit may include a YC separation unit performingfiltering to separate the predicted value of the composite video burstsignal into an in-phase signal and an orthogonal-phase signal by using aYC separation filter of a type different from that of a YC separationfilter for separating a luminance signal and a chrominance signal in asystem decoder, a color demodulation unit separating the chrominancesignal into an in-phase signal and an orthogonal-phase signal, and aYIQ-RGB color space transform unit transforming the luminance signal,the in-phase signal and the orthogonal-phase signal into an R signal, aG signal, and a B signal, respectively, in RGB space and thus into apredicted value of the input video signal.

The apparatus may further include an artifact detection and removal unitdetecting and removing an artifact of the output video signal, whereinthe artifact detection and removal unit includes an RGB-YIQ color spacetransform unit transforming the output video signal into a luminancesignal, an in-phase signal and an orthogonal-phase signal, a colormodulation unit synthesizing the in-phase signal and the orthogonalsignal into a chrominance signal, a YC addition unit synthesizing theluminance signal and the synthesized chrominance signal into a compositevideo burst signal, an artifact detection map generation unit generatingan artifact detection map indicating an area where an artifact occurs bycomparing the luminance signal and a signal obtained by low passfiltering the composite video burst signal, and an artifact removal unitremoving artifacts by decoding the composite video burst signalaccording to the artifact detection map.

The artifact removal unit may include a YC separation unit performingfiltering to separate the area where the artifact is detected accordingto the artifact detection map, into a luminance signal and a chrominancesignal by using a YC separation filter of a type different from that ofa YC separation filter for separating a luminance signal and achrominance signal in a system decoder, a color demodulation unitseparating the chrominance signal into an in-phase signal and anorthogonal-phase signal, and a YIQ-RGB color space transform unittransforming the luminance signal, the in-phase signal and theorthogonal-phase signal into an R signal, a G signal, and a B signal,respectively, in RGB space, and outputting an artifact-free signal.

The apparatus may further include an artifact detection and removal unitdetecting and removing an artifact of the output video signal, whereinthe artifact detection and removal unit includes a motion area detectionunit which estimates a motion vector from two neighboring frames in theoutput video signal, generates a motion detection map indicating whethermotion exists between two neighboring frames and a motion compensationmap indicating whether a motion compensation filter is used based on themotion vector, an artifact detection unit generating a dot crawlartifact map by detecting a dot crawl artifact that is a dot crawloccurring in the vicinity of an outline of an image, or generating arainbow effect detection map by detecting a rainbow effect in whichrainbow colors are seen in an area where a big difference of brightnessoccurs when an image moves fast, a motion compensation unit compensatingfor a motion according to the motion compensation map, and amultiplexing unit filtering the area where the artifact occurs bycombining a time filter and a space filter based on control signals ofthe motion detection map, the motion compensation map, the dot crawlartifact detection map in a current frame, the dot crawl artifactdetection map in the previous frame, and the rainbow effect detectionmap.

According to another aspect of the present invention, there is providedan apparatus for detecting and removing an artifact in a composite videoburst signal, including an encoder prediction unit encoding an outputvideo signal and outputting a predicted value of a composite video burstsignal, and a decoder prediction unit decoding the output predictedvalue of the composite video burst signal and outputting a predictedvalue of an input video signal.

The decoder prediction unit may include a YC separation unit performingfiltering to separate the predicted value of the composite video burstsignal into a luminance signal, an in-phase signal and anorthogonal-phase signal by using a YC separation filter of a typedifferent from that of a YC separation filter for separating a luminancesignal and a chrominance signal in a system decoder, a colordemodulation unit separating the chrominance signal into an in-phasesignal and an orthogonal-phase signal, and a YIQ-RGB color spacetransform unit transforming the luminance signal, the in-phase signaland the orthogonal-phase signal into an R signal, a G signal, and a Bsignal, respectively, in RGB space and thus into a predicted value ofthe input video signal.

According to another aspect of the present invention, there is providedan apparatus for detecting and removing an artifact in a composite videoburst signal including an RGB-YIQ color space transform unittransforming an output video signal into a luminance signal, an in-phasesignal and an orthogonal-phase signal, a color modulation unitsynthesizing the in-phase signal and the orthogonal signal into achrominance signal, a YC addition unit synthesizing the luminance signaland the synthesized chrominance signal into a composite video burstsignal, an artifact detection map generation unit generating an artifactdetection map indicating an area where an artifact occurs by comparingthe luminance signal and a signal obtained by low pass filtering thecomposite video burst signal, and an artifact removal unit removingartifacts by decoding the composite video burst signal according to theartifact detection map.

The artifact removal unit may include a YC separation unit performingfiltering to separate the area where the artifact is detected accordingto the artifact detection map into a luminance signal and a chrominancesignal by using a YC separation filter of a type different from that ofa YC separation filter for separating a luminance signal and achrominance signal in a system decoder, a color demodulation unitseparating the chrominance signal into an in-phase signal and anorthogonal-phase signal, and a YIQ-RGB color space transform unittransforming the luminance signal, the in-phase signal and theorthogonal-phase signal into an R signal, a G signal, and a B signal,respectively, in RGB space, and outputting an artifact-free signal.

According to another aspect of the present invention, there is providedan apparatus for detecting and removing an artifact in a composite videoburst signal including a motion area detection which estimates a motionvector from two neighboring frames in the output video signal, generatesa motion detection map indicating whether motion exists between twoneighboring frames and a motion compensation map indicating whether amotion compensation filter is used based on the motion vector, anartifact detection unit generating a dot crawl artifact map by detectinga dot crawl artifact that is a dot crawl occurring in the vicinity of anoutline of an image, or generating a rainbow effect detection map bydetecting a rainbow effect in which rainbow colors are seen in an areawhere a big difference of brightness occurs when an image moves fast, amotion compensation unit compensating for a motion according to themotion compensation map, and a multiplexing unit filtering the areawhere the artifact occurs by combining a time filter and a space filterbased on control signals of the motion detection map, the motioncompensation map, the dot crawl artifact detection map in a currentframe, the dot crawl artifact detection map in the previous frame, andthe rainbow effect detection map.

The motion area detection unit may estimate a motion by using thedifference between brightness values of a current frame block and theprevious frame block, and generate a motion detection map indicating thepresence of a motion. A motion compensation unit may indicate whether amotion is compensated for.

The time filter may remove an artifact of the composite video burstsignal by performing time filtering of an artifact in an area where nomotion exists or by performing time filtering of an artifact in an areawhere a motion exists after compensating for a motion.

The space filter may perform space filtering using the followingequation, or with a filter using a neural network circuit:

${\hat{F}\left( {x,y,{;t}} \right)}_{spatial} = {\frac{\begin{matrix}{{F\left( {{x - 1},{y;t}} \right)} + {F\left( {{x + 1},{y;t}} \right)} +} \\{{F\left( {x,{{y - 1};t}} \right)} + {F\left( {x,{{y + 1};t}} \right)}}\end{matrix}}{4}.}$

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a block diagram illustrating a related art apparatus forimproving picture quality;

FIG. 2 is a graph illustrating the frequency characteristic of acomposite video burst signal;

FIG. 3 is a block diagram illustrating a structure of an apparatus forimproving picture quality according to an exemplary embodiment of thepresent invention;

FIG. 4 is a flowchart illustrating a method of improving picture qualityaccording to an exemplary embodiment of the present invention;

FIG. 5 is a flowchart illustrating preprocessing according to anexemplary embodiment of the present invention;

FIG. 6 is a graph illustrating a process of a preprocessing filteraccording to an exemplary embodiment of the present invention;

FIG. 7 is a block diagram illustrating a structure of an apparatus fordetecting and removing artifacts according to an exemplary embodiment ofthe present invention;

FIG. 8A is a block diagram illustrating a structure of an encoderaccording to an exemplary embodiment of the present invention;

FIG. 8B is a block diagram illustrating a structure of a decoderaccording to an exemplary embodiment of the present invention;

FIG. 9 is a flowchart illustrating a method of detecting and removingartifacts according to an exemplary embodiment of the present invention;

FIG. 10 is a block diagram illustrating a structure of an apparatus fordetecting and removing artifacts according to another exemplaryembodiment of the present invention;

FIG. 11 is a flowchart illustrating a method of detecting and removingartifacts according to another exemplary embodiment of the presentinvention;

FIG. 12 is a block diagram illustrating a structure of an apparatus fordetecting and removing artifacts according to still another exemplaryembodiment of the present invention;

FIG. 13 is a flowchart illustrating a method of detecting and removingartifacts according to still another exemplary embodiment of the presentinvention;

FIG. 14 is a diagram illustrating an operation used to detect a motionaccording to an exemplary embodiment of the present invention;

FIG. 15 is a diagram illustrating a method of detecting a dot crawlartifact according to an exemplary embodiment of the present invention;

FIG. 16 is a diagram illustrating a method of detecting a rainbow effectaccording to an exemplary embodiment of the present invention;

FIG. 17 is a diagram illustrating a time filter of FIG. 12 according toan exemplary embodiment of the present invention;

FIG. 18 is a diagram illustrating a space filter of FIG. 12 according toan exemplary embodiment of the present invention;

FIG. 19 is a diagram illustrating a multiplexing unit of FIG. 12according to an exemplary embodiment of the present invention; and

FIG. 20 is a table illustrating the relations between control signals ofthe multiplexing unit and filters according to an exemplary embodimentof the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown.

As illustrated in FIG. 2, a composite video burst signal includes anin-phase signal (I signal) and an orthogonal-phase signal (Q signal)with a color subcarrier frequency Fsc (3.58 Mhz) at the center.Accordingly, the composite video burst signal has a form in which aluminance signal, an in-phase signal and an orthogonal-phase signal areadded as shown in equation 1 below. The luminance signal (Y signal) ispositioned in low frequency bands and the chrominance signal (C signal)is positioned in high frequency bands:

$\begin{matrix}{{CVBS} = {{Y + C} = {Y + {I\;{\cos\left( {F_{sc}t} \right)}} + {Q\;{\sin\left( {F_{sc}t} \right)}}}}} & (1)\end{matrix}$

Thus, the composite video burst signal has much information in the lowfrequency bands but also has much information around 3.58 Mhz where thechrominance signal is positioned. Accordingly, the ordinary noiseremoval technique by which a high frequency band is removed or energy isreduced in an ordinary signal processing process may damage thechrominance signal.

FIG. 3 is a block diagram illustrating a structure of an apparatus forimproving picture quality according to an exemplary embodiment of thepresent invention. Referring to FIG. 3, the apparatus for improvingpicture quality is composed of a preprocessing filter 310, a decoder320, and an artifact detection and removal unit 330. For convenience ofexplanation, a system encoder 302 is also shown.

If an input video signal X is input, the system encoder 302 encodes theinput video signal X and outputs a composite video burst signalX_(CVBS).

The preprocessing filter 310 is composed of a low pass filter 312, ahigh pass filter 314, a wavelet packet filter 316, and a Wiener filter318.

The low pass filter 312 and the high pass filter 314 divide thecomposite video burst signal X_(CVBS) into a plurality of frequencybands.

The wavelet packet filter 316 further divides each band having achrominance signal energy equal to or higher than a specified thresholdinto smaller bands, and among the further divided bands, the waveletpacket filter 316 removes a signal in each band having energy lower thana specified threshold.

The Wiener filter 318 performs Wiener filtering of each band having achrominance signal energy lower than a specified threshold and thusremoves noise.

The operations of the preprocessing filter 310 will be explained laterin more detail with reference to FIGS. 5 and 6.

The decoder 320 is composed of a YC separation unit 322, a colordemodulation unit 324, and a YIQ-RGB color space transform unit 326.

The YC separation unit 322 separates the filtered composite video burstsignal X′_(CVBS) into a luminance signal and a chrominance signal.

The color demodulation unit 324 separates the chrominance signal into anin-phase signal and an orthogonal-phase signal.

The YIQ-RGB color space transform unit 326 transforms the luminancesignal, the in-phase signal and the orthogonal-phase signal into an Rsignal, a G signal and a B signal, respectively, and outputs an outputvideo signal.

The artifact detection and removal unit 330 detects an artifact of theoutput video signal X′, removes the detected artifact, and outputs anartifact-free signal, X″. The process of detecting and removing theartifact will be explained later with reference to FIGS. 7 through 20.

FIG. 4 is a flowchart illustrating a method of improving picture qualityaccording to an exemplary embodiment of the present invention. Referringto FIG. 4, the method of improving picture quality will now beexplained.

In operation 402, if the input video signal X is encoded into acomposite video burst signal X_(CVBS) and transmitted, preprocessing ofthe composite video burst signal X_(CVBS) is performed. Thepreprocessing will be explained later with reference to FIGS. 5 and 6.

In operation 404, the composite video burst signal X_(CVBS) is separatedinto a luminance signal and a chrominance signal.

In operation 406, the chrominance signal is separated into an in-phasesignal and an orthogonal phase signal.

In operation 408, the luminance signal, the in-phase signal and theorthogonal-phase signal are transformed into an R signal, a G signal anda B signal, respectively, on an RGB plane and an output video signal X′is output.

In operation 410, an artifact of the output video signal X′ is detectedand removed. The method of detecting and removing an artifact can beperformed in a variety of ways, which will be explained later withreference to FIGS. 7 through 20.

FIG. 5 is a flowchart illustrating preprocessing according to anexemplary embodiment of the present invention.

In operation 502, the composite video burst signal X_(CVBS) is separatedinto a plurality of bands.

FIG. 6 is a graph illustrating a process of a preprocessing filteraccording to an exemplary embodiment of the present invention. Referringto FIG. 6, the process of separating the composite video burst signalX_(CVBS) into a plurality of bands will now be explained.

First, the composite video burst signal X_(CVBS) is filtered through alow pass filter and a high pass filter.

As a result of the filtering, the signal X_(CVBS) is separated into ahigh frequency band including LLL, LLH, LHL, and LHH bands, and a lowfrequency band including HLL, HLH, HHL, and HHH bands.

If the frequency bands are again separated using a low pass filter and ahigh pass filter, the low frequency band is separated into a bandincluding LLL and LLH bands and a band including LHL and LHH bands, andthe high frequency band is separated into a band including HHL and HHHbands and a band including HHL and HHH bands.

Finally, the frequency bands are again separated using a low pass filterand a high pass filter, and eight separated bands, including LLL, LLH,LHL, LHH, HLL, HLH, HHL, and HHH bands, are obtained.

In operation 504, among the separated frequency bands, each band havinga chrominance signal energy equal to or higher than a specifiedthreshold is further divided into a plurality of bands.

Referring to FIG. 6, LHL and HLL bands are bands that have a chrominancesignal energy equal to or higher than a specified threshold, and thesebands are once more separated into four or more bands. Here, the bandshaving a chrominance signal energy equal to or higher than the specifiedthreshold are generally distributed in the vicinity of 3.58 MHz, whichis an eigenfrequency of a chrominance signal that is from about 2.5 MHzto 5 MHz. However, the threshold may be applied differently in otherexemplary embodiments.

In operation 506, among the further divided plurality of bands, a signalin each band having energy less than a specified threshold is removed.

In order to perform the removal function, a best basis algorithm is usedin the current exemplary embodiment of the present invention.

In the best basis algorithm, it is assumed that a wavelet transform isB={W_(p)}_(1≦p≦N), and when a wavelet transform coefficient is <x,W_(p)>, only a signal satisfying equation 2 below is restored using B,with respect to a threshold T corresponding to a purpose such ascompression or noise removal. Here, restoration means that a signal of aband having a size less than the threshold T is removed by setting thesize to 0, and only the remaining signals are used.|<x,W_(p)>|>T  (2)

That is, by applying the wavelet transform B={W_(p)}_(1≦p≦N) to each ofthe signals of the plurality of separated bands, wavelet coefficients<x, W_(p)> are generated, and in relation to the signal of a frequencyband having a generated wavelet coefficient whose absolute value is lessthan the specified threshold, the size of the signal is set to 0 andthus is removed. These signals are removed since the composite videoburst signal X_(CVBS) is a signal before decoding is performed and asignal in which noise, such as white Gaussian noise, has been added toall bands. Accordingly, a frequency band having less energy is thoughtto indicate that when the signal of the frequency band is decoded, noisehas more influence than the signal.

Further, T varies with respect to the purpose of using the waveletpacket. In the case of compression, T is set to have a small value tominimize damage to information. In the case of noise removal, a valuegreater than that in the case of compression is used considering thedistribution and the characteristic of the signal. However, a differentvalue may be employed as the threshold in other exemplary embodiments.

In operation 508, Wiener filtering of the bands having a chrominancesignal energy lower than the specified threshold is performed.

Referring to FIG. 6, Wiener filtering is performed with respect to LLL,LLH, LHL, HLH, HHL, and HHH bands, excluding LHH and HLL bands.

Assuming that a signal from which noise should be removed is g, a localmean is

${m_{g} = {\frac{1}{\left( {{2W} + 1} \right)}\underset{i = {- n}}{\overset{i = n}{Q}}{g(i)}}},$and a noise-removed signal is {circumflex over (f)}, the Wienerfiltering is defined in equation 3 below:

$\begin{matrix}{{{\hat{f}(i)} = m_{g}},{\frac{\sigma^{2} - v^{2}}{\sigma^{2}}\left( {{g(i)} - m_{g}} \right)}} & (3)\end{matrix}$where i is the size of a mask. Also, v of equation 3 represents noisedispersion, and is the dispersion of a signal obtained by subtractingthe local mean mg from a signal g in which noise is included. By usingequation 3, noise can be removed while protecting an edge component. Thedegree of protection of the edge component and the degree of noiseremoval can be adjusted by changing the size of the mask.

Referring to FIG. 6, a large amount of video information is modulatedonto LLL and LLH bands, and in each band a signal component is muchlarger than noise. Accordingly, in order to remove noise whileprotecting signals in the bands as much as possible, the size of a maskis reduced. For example, the size of the mask can be set to 9 pixels. Inthis case, the range of i in the local mean

$m_{g} = {\frac{1}{\left( {{2W} + 1} \right)}\underset{i = {- n}}{\overset{i = n}{Q}}{g(i)}}$will be determined to be from −4 to 4.

LHL and HLH bands are in the vicinity of an eigenfrequency at which thechrominance signal is modulated, and have the high frequency componentof the video signal. However, since the ratio of noise in LHL and HLHbands is higher than that in LLL and LLH bands, in order to increase theeffect of noise removal the size of a mask is set to be bigger than thatfor LLL and LLH bands. For example, the size of the mask can bedetermined to be 49 pixels.

HHL and HHH bands take up the smallest portion of the entire compositevideo burst signal, while noise in HHL and HHH bands takes up a greaterportion compared to the signal components. Accordingly, the size of amask is set to be largest in the HHL and HHH bands. For example, thesize of the mask can be determined to be about 79 pixels.

After filtering is performed with varying sizes of masks with respect torespective bands, the filtered bands are combined into one signal. Inthis way, noise can be removed while protecting signal components asmuch as possible. In this process, the smaller the size of the mask, themore the edge components can be protected, and the bigger the size ofthe mask, the more noise can be removed.

However, the size of the mask is not limited to the values describedabove and different values may be applied with respect to differentexemplary embodiments.

Thus far in the process according to the exemplary embodiments of thepresent invention as described above, preprocessing of the compositevideo burst signal X_(CVBS) is performed using the wavelet packet filterand Wiener filter, and by decoding the preprocessed signal X′_(CVBS),the output video signal X″ from which noise has been removed is output.

A process of further removing artifacts in the output video signal X″will now be explained.

FIG. 7 is a block diagram illustrating a structure of an apparatus fordetecting and removing artifacts according to an exemplary embodiment ofthe present invention. Referring to FIG. 7, the apparatus for detectingand removing artifacts is composed of an encoder prediction unit 732 anda decoder prediction unit 734. A system encoder 710 and a system decoder720 are illustrated to explain the current exemplary embodiment. Also,the apparatus for detecting and removing artifacts according to thecurrent exemplary embodiment can be applied to the artifact detectionand removal unit 330 of FIG. 3.

FIG. 8A is a block diagram illustrating a structure of an encoderaccording to an exemplary embodiment of the present invention. Referringto FIG. 8A, system encoder 710 is composed of an RGB-YIQ color spacetransform unit 712, a color modulation unit 714, and a YC addition unit716.

The RGB-YIQ color space transform unit (E₁) 712 transforms an RGB signalinto a YIQ signal and the transform process is defined in equation 4below:

$\begin{matrix}{{x_{YIQ} = {E_{1}x}},{{E_{1}{{\text{:}\left\lbrack {{RGB}\mspace{14mu}{to}\mspace{14mu}{YIQ}\mspace{14mu}{color}\mspace{14mu}{space}\mspace{20mu}{conversion}} \right\rbrack}\begin{bmatrix}Y_{0} \\I_{0} \\Q_{0} \\\vdots \\Y_{{MN} - 1} \\I_{{MN} - 1} \\Q_{{MN} - 1}\end{bmatrix}}} = {\begin{bmatrix}E_{1}^{sub} & O_{3 \times 3} & \cdots & O_{3 \times 3} \\O_{3 \times 3} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{3 \times 3} \\O_{3 \times 3} & \cdots & O_{3 \times 3} & E_{1}^{sub}\end{bmatrix}\begin{bmatrix}R_{0} \\G_{0} \\B_{0} \\\vdots \\R_{{MN} - 1} \\G_{{MN} - 1} \\B_{{MN} - 1}\end{bmatrix}}}} & (4)\end{matrix}$where Q_(max) is an m×n zero matrix and a submatrix E₁ ^(sub) is definedin equation 5 below:

$\begin{matrix}{{E_{1}^{sub} = \begin{bmatrix}0.299 & 0.587 & 0.114 \\0.596 & {- 0.275} & {- 0.321} \\0.212 & {- 0.523} & 0.311\end{bmatrix}},{E_{1}^{sub}\text{:}3 \times 3}} & (5)\end{matrix}$

The color modulation unit (E₂) performs a quadrature amplitudemodulation (QAM) function for generating a chrominance signal bycombining an in-phase signal and an orthogonal-phase signal. Themodulation process is defined in equation 6 below:

${x_{YC} = {E_{2}x_{YIQ}}},{{E_{2}{{\text{:}\left\lbrack {{color}\mspace{14mu}{modulation}} \right\rbrack}\begin{bmatrix}Y_{0} \\C_{0} \\\vdots \\Y_{{MN} - 1} \\C_{{MN} - 1}\end{bmatrix}}} = {\begin{bmatrix}E_{2}^{sub} & O_{4M \times 6M} & \cdots & O_{4M \times 6M} \\O_{4M \times 6M} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{2M \times 3M} \\O_{4M \times 6M} & \cdots & O_{4M \times 6M} & E_{2}^{sub}\end{bmatrix}\begin{bmatrix}Y_{0} \\I_{0} \\Q_{0} \\\vdots \\Y_{{MN} - 1} \\I_{{MN} - 1} \\Q_{{MN} - 1}\end{bmatrix}}}$where the submatrix E₂ ^(sub) is defined equation 7 below:

$\begin{matrix}{{E_{2}^{sub} = \begin{bmatrix}E_{2}^{sub\_ odd} & O_{2M \times 3M} \\O_{2M \times 3M} & E_{2}^{sub\_ even}\end{bmatrix}},{E_{2}^{sub}\text{:}\mspace{14mu} 4M \times 6M}} & (7)\end{matrix}$

Also, submatrices E₂ ^(sub) ^(—) ^(odd) and E₂ ^(sub) ^(—) ^(even) aredefined in equations 8 and 9 below, respectively:

$\begin{matrix}{{E_{2}^{sub\_ odd} = {{\begin{bmatrix}E_{2}^{sub\_ oddline} & O_{8 \times 12} & \cdots & O_{8 \times 12} \\O_{8 \times 12} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{8 \times 12} \\O_{8 \times 12} & \cdots & O_{8 \times 12} & E_{2}^{sub\_ oddline}\end{bmatrix}.\mspace{14mu} E_{2}^{sub\_ odd}}:\mspace{14mu} 2M \times 3M}},} & (8) \\{{E_{2}^{sub\_ even} = \begin{bmatrix}E_{2}^{sub\_ evenline} & O_{8 \times 12} & \cdots & O_{8 \times 12} \\O_{8 \times 12} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{8 \times 12} \\O_{8 \times 12} & \cdots & O_{8 \times 12} & E_{2}^{sub\_ evenline}\end{bmatrix}},{E_{2}^{sub\_ even}\text{:}\mspace{14mu} 2M \times 3M}} & (9)\end{matrix}$

Also, submatrices E₂ ^(sub) ^(—) ^(oddline) and E₂ ^(sub) ^(—)^(evenline) are defined in equations 10 and 11 below, respectively:

$\begin{matrix}{{E_{2}^{sub\_ oddline} = \begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & {- 1} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & {- 1}\end{bmatrix}},{E_{2}^{sub\_ oddline}:\mspace{14mu} 8 \times 12},} & (10) \\{E_{2}^{sub\_ evenline} = {\quad{{\begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & {- 1} & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & {- 1} & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1\end{bmatrix}.\mspace{14mu} E_{2}^{sub\_ evenline}}\text{:}\mspace{14mu} 8 \times 12}}} & (11)\end{matrix}$

The YC addition unit (E₃) 716 performs an interleaving function foradding a luminance signal and a chrominance signal. The interleavingprocess is defined in equation 12 below:

$\quad\begin{matrix}\begin{matrix}{{x_{CVBS} = {E_{3}x_{YC}}},} \\{\begin{bmatrix}{Y_{0} + C_{0}} \\\vdots \\{Y_{{MN} - 1} + C_{{MN} - 1}}\end{bmatrix} = {\begin{bmatrix}E_{3}^{sub} & O_{2 \times 4} & \cdots & O_{2 \times 4} \\O_{2 \times 4} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{2 \times 4} \\O_{2 \times 4} & \cdots & O_{2 \times 4} & E_{3}^{sub}\end{bmatrix}\begin{bmatrix}Y_{0} \\C_{0} \\\vdots \\Y_{{MN} - 1} \\C_{{MN} - 1}\end{bmatrix}}}\end{matrix} & (12)\end{matrix}$where submatrix E₃ ^(sub) is defined in equation 13 below:

$\begin{matrix}{{E_{3}^{sub} = \begin{bmatrix}1 & 1 & 0 & 0 \\0 & 0 & 1 & 1\end{bmatrix}},{E_{3}^{sub}\text{:}\mspace{14mu} 2 \times 4}} & (13)\end{matrix}$

FIG. 8B is a block diagram illustrating a structure of a decoderaccording to an exemplary embodiment of the present invention. Referringto FIG. 8B, the system decoder 720 is composed of a YC separation unit722, a color demodulation unit 724, and a YIQ-RGB color space transformunit 726.

The YC separation unit (D₃) 722 separates an input signal into aluminance signal and a chrominance signal, by using a YC separationfilter, and the shape of the YC separation unit (D₃) 7 varies dependingon the type of a YC separation filter. When the YC separation filter isa low pass filter (LPF), the separation process is defined in equation14 below:

$\begin{matrix}{{x_{YC}^{\prime} = {D_{3,L}x_{CVBS}}},{{D_{3,L}{{\text{:}\mspace{14mu}\lbrack{LPF}\rbrack}\left\lbrack \begin{matrix}o_{4 \times 1} \\Y_{4}^{\prime} \\C_{4}^{\prime} \\\vdots \\Y_{{MN} - 5}^{\prime} \\C_{{MN} - 5}^{\prime} \\o_{4 \times 1}\end{matrix} \right\rbrack}} = {\left\lbrack \begin{matrix}d_{4} & d_{5} & \cdots & d_{{MN} - 1} & d_{0} & \cdots & d_{3} \\d_{3} & d_{4} & \cdots & d_{{MN} - 2} & d_{{MN} - 1} & \cdots & d_{2} \\\vdots & \vdots & \cdots & \vdots & \vdots & \cdots & \vdots \\d_{5} & d_{6} & \cdots & d_{0} & d_{1} & \cdots & d_{4}\end{matrix} \right\rbrack{\quad\left\lbrack \begin{matrix}{Y_{0} + C_{0}} \\\vdots \\{Y_{{MN} - 1} + C_{{MN} - 1}}\end{matrix} \right\rbrack}}}} & (14)\end{matrix}$where vector d_(i) (i=0, 1, . . . , MN−1) forming D₃ is defined inequation 15 below:

$\begin{matrix}{{d_{0} = {\begin{bmatrix}{- 0.0489} \\0.0489\end{bmatrix} = d_{8}}},{d_{1} = {\begin{bmatrix}{- 0.0654} \\0.0654\end{bmatrix} = d_{7}}},{d_{2} = {\begin{bmatrix}0.0751 \\{- 0.0751}\end{bmatrix}d_{6}}},{d_{3} = {\begin{bmatrix}0.3180 \\{- 0.3180}\end{bmatrix} = d_{5}}},{d_{4} = \begin{bmatrix}0.4423 \\{1 - 0.4423}\end{bmatrix}},{d_{9} = {\begin{bmatrix}0 \\0\end{bmatrix} = {d_{10} = {\cdots\; = \; d_{{MN} - 1}}}}}} & (15)\end{matrix}$

In this case, the coefficients are those used when a 9-tap low passfilter with a cutoff frequency of 3 MHz is used. With respect to otherembodiments, other filters, such as 1H comb filter and 2H comb filter,can be employed selectively as the YC separation filter, and accordingto the filters, the coefficient values also vary.

The color demodulation unit (D₂) 724 separates a chrominance signal intoan in-phase signal and an orthogonal-phase signal, and the separationprocess is defined in equation 16 below:

$\begin{matrix}{{x_{YIQ}^{\prime} = {D_{2}x_{YC}^{\prime}}},{D_{2} = {{D_{2,L}{D_{2,{demo}}\begin{bmatrix}Y_{0}^{\prime} \\I_{0}^{\prime} \\Q_{0}^{\prime} \\\vdots \\Y_{{MN} - 1}^{\prime} \\I_{{MN} - 1}^{\prime} \\Q_{{MN} - 1}^{\prime}\end{bmatrix}}} = {{{D_{2,L}\begin{bmatrix}D_{2,{demo}}^{sub} & O_{6M \times 4M} & \cdots & O_{6M \times 4M} \\O_{6M \times 4M} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{6M \times 4M} \\O_{6M \times 4M} & \cdots & O_{6M \times 4M} & D_{2,{demo}}^{sub}\end{bmatrix}}\begin{bmatrix}Y_{0}^{\prime} \\C_{0}^{\prime} \\\vdots \\Y_{{MN} - 1}^{\prime} \\C_{{MN} - 1}^{\prime}\end{bmatrix}} = {D_{2,L}\begin{bmatrix}Y_{0,{demo}}^{\prime} \\I_{0,{demo}}^{\prime} \\Q_{0,{demo}}^{\prime} \\\vdots \\Y_{{{MN} - 1},{demo}}^{\prime} \\I_{{{MN} - 1},{demo}}^{\prime} \\Q_{{{MN} - 1},{demo}}^{\prime}\end{bmatrix}}}}}} & (16)\end{matrix}$

Here, D_(2,demo) ^(sub) as an inverse process of E₂ ^(sub) is defined inequation 17 below:

$\begin{matrix}{D_{2,{demo}}^{sub} = {{\begin{bmatrix}D_{2,{demo}}^{sub\_ odd} & O_{3M \times 2M} \\O_{3M \times 2M} & D_{2,{demo}}^{sub\_ even}\end{bmatrix}.\mspace{14mu} D_{2,{demo}}^{sub}}\text{:}\mspace{14mu} 6M \times 4M}} & (17)\end{matrix}$

Here, submatrices D_(2,demo) ^(sub) ^(—) ^(odd) and D_(2,demo) ^(sub)^(—) ^(even) are defined in equations 18 and 19 below, respectively:

$\begin{matrix}{{D_{2,{demo}}^{sub\_ odd} = \begin{bmatrix}D_{2,{demo}}^{sub\_ oddline} & O_{12 \times 8} & \cdots & O_{12 \times 8} \\O_{12 \times 8} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{12 \times 8} \\O_{12 \times 8} & \cdots & O_{12 \times 8} & D_{2,{demo}}^{sub\_ oddline}\end{bmatrix}},{D_{2,{demo}}^{sub\_ oddline}\text{:}\mspace{14mu} 3M \times 2M},} & (18) \\{{D_{2,{demo}}^{sub\_ even} = \begin{bmatrix}D_{2,{demo}}^{sub\_ evenline} & O_{12 \times 8} & \cdots & O_{12 \times 8} \\O_{12 \times 8} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{12 \times 8} \\O_{12 \times 8} & \cdots & O_{12 \times 8} & D_{2,{demo}}^{sub\_ evenline}\end{bmatrix}},{D_{2,{demo}}^{sub\_ evenline}\text{:}\mspace{14mu} 3M \times 2M}} & (19)\end{matrix}$

Also, D_(2,demo) ^(sub) ^(—) ^(oddline) and D_(2,demo) ^(sub) ^(—)^(evenline) are defined in equation 20 below:

$\begin{matrix}{{{D_{2,{demo}}^{sub\_ oddline} = \begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & {- 1} & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & {- 1}\end{bmatrix}},{D_{2,{demo}}^{sub\_ evenline} = \begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & {- 1} & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & {- 1} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & 1\end{bmatrix}}}D_{2,{demo}}^{sub\_ oddline},{D_{2,{demo}}^{sub\_ evenline}\text{:}\mspace{14mu} 12 \times 8}} & (20)\end{matrix}$

D_(2,L) performing low pass filtering of an in-phase signal and anorthogonal-phase signal is defined in equation 21 below:

$\quad\begin{matrix}\begin{matrix}{\begin{bmatrix}o_{4 \times 1} \\Y_{0}^{\prime} \\I_{0}^{\prime} \\Q_{0}^{\prime} \\\vdots \\Y_{{MN} - 1}^{\prime} \\I_{{MN} - 1}^{\prime} \\Q_{{MN} - 1}^{\prime} \\o_{4 \times 1}\end{bmatrix} = {D_{2,L}\begin{bmatrix}Y_{0,{demo}}^{\prime} \\I_{0,{demo}}^{\prime} \\Q_{0,{demo}}^{\prime} \\\vdots \\Y_{{{MN} - 1},{demo}}^{\prime} \\I_{{{MN} - 1},{demo}}^{\prime} \\Q_{{{MN} - 1},{demo}}^{\prime}\end{bmatrix}}} \\{= \begin{bmatrix}D_{4} & D_{5} & \cdots & D_{{MN} - 1} & D_{0} & \cdots & D_{3} \\D_{3} & D_{4} & \cdots & D_{{MN} - 2} & D_{{MN} - 1} & \cdots & D_{2} \\\vdots & \vdots & \cdots & \vdots & \vdots & \cdots & \vdots \\D_{5} & D_{6} & \cdots & D_{0} & D_{1} & \cdots & D_{4}\end{bmatrix}} \\{\begin{bmatrix}Y_{0,{demo}}^{\prime} \\I_{0,{demo}}^{\prime} \\Q_{0,{demo}}^{\prime} \\\vdots \\Y_{{{MN} - 1},{demo}}^{\prime} \\I_{{{MN} - 1},{demo}}^{\prime} \\Q_{{{MN} - 1},{demo}}^{\prime}\end{bmatrix}}\end{matrix} & (21)\end{matrix}$

Vector D_(i) (i=0, 1, . . . , MN−1) forming D_(2,L) is defined inequation 22 below:

$\begin{matrix}{{D_{0} = {\begin{bmatrix}0 & 0 & 0 \\0 & 0.0245 & 0 \\0 & 0 & 0.0807\end{bmatrix} = D_{8}}},{D_{1} = {\begin{bmatrix}0 & 0 & 0 \\0 & 0.0732 & 0 \\0 & 0 & 0.1017\end{bmatrix} = D_{7}}},{D_{2} = {\begin{bmatrix}0 & 0 & 0 \\0 & 0.1298 & 0 \\0 & 0 & 0.1192\end{bmatrix} = D_{6}}},{D_{3} = {\begin{bmatrix}0 & 0 & 0 \\0 & 0.1758 & 0 \\0 & 0 & 0.1309\end{bmatrix} = D_{5}}},{D_{4} = \begin{bmatrix}1 & 0 & 0 \\0 & 0.1934 & 0 \\0 & 0 & 0.1350\end{bmatrix}},{D_{9} = {O_{3 \times 3} = {D_{10} = {\cdots = D_{{MN} - 1}}}}}} & (22)\end{matrix}$

The YIQ-RGB space transform unit (D₁) 726 transforms a YIQ signal intoan RGB signal and outputs an output image signal, and this transformprocess is defined in equation 23 below:

$\begin{matrix}{{D_{1}\begin{bmatrix}R_{0}^{\prime} \\G_{0}^{\prime} \\B_{0}^{\prime} \\\vdots \\R_{{MN} - 1}^{\prime} \\G_{{MN} - 1}^{\prime} \\B_{{MN} - 1}^{\prime}\end{bmatrix}} = {\begin{bmatrix}D_{1}^{sub} & O_{3 \times 3} & \cdots & O_{3 \times 3} \\O_{3 \times 3} & \ddots & \; & \vdots \\\vdots & \; & \ddots & O_{3 \times 3} \\O_{3 \times 3} & \cdots & O_{3 \times 3} & D_{1}^{sub}\end{bmatrix}\begin{bmatrix}Y_{0}^{\prime} \\I_{0}^{\prime} \\Q_{0}^{\prime} \\\vdots \\Y_{{MN} - 1}^{\prime} \\I_{{MN} - 1}^{\prime} \\Q_{{MN} - 1}^{\prime}\end{bmatrix}}} & (23)\end{matrix}$

Submatrix D₁ ^(sub) is defined in equation 24 below:

$\begin{matrix}{{D_{1}^{sub} = \begin{bmatrix}1 & 0.956 & 0.620 \\1 & {- 0.272} & {- 0.647} \\1 & {- 1.108} & 1.7\end{bmatrix}},{D_{1}^{sub}\text{:}\mspace{14mu} 3 \times 3}} & (24)\end{matrix}$

As described above, in the process of encoding and decoding using thesystem encoder 710 and the system decoder 720, artifacts occur in thecomposite video burst signal. Also, even in the signal decoded throughthe preprocessing process as illustrated in FIG. 3, some artifactsremain. A process of removing the artifacts that occur in the processwill now be explained.

The encoder prediction unit 732 performs a function for restoring thecomposite video burst signal X_(CVBS) from the output video signal X′before the decoding is performed. The value obtained through the encoderprediction unit 732 is a predicted value X′_(CVBS) that is close to thecomposite video burst signal.

The decoder prediction unit 734 decodes the encoded predicted value,X′_(CBS), by using a YC separation filter of a type different from thatof the YC separation filter used in the system decoder 720. By doing so,the decoder prediction unit 734 outputs a predicted value, {tilde over(x)}, in which artifacts not removed in the system decoder 720 areremoved.

For example, if a 2H comb filter is used as a YC separation filter inthe system decoder 720, artifacts in the length direction are removedbut artifacts in the width direction are generated. Here, if a 3H combfilter is used as a YC separation filter in the decoder prediction unit734, the 3H comb filter has a function for removing artifacts in thewidth direction and thus removes the artifacts in the width directiongenerated through the 2H comb filter and the already-existing originalartifacts in the width direction.

FIG. 9 is a flowchart illustrating a method of detecting and removingartifacts according to an exemplary embodiment of the present invention.

In operation 902, if an input video signal X is input, the input videosignal X is encoded and a composite video burst signal X_(CVBS) isoutput.

In operation 904, the composite video burst signal X_(CVBS) is decodedand an output video signal X′ is output.

In operation 906, the output video signal X′ is encoded and a predictedvalue, X′_(CVBS), of the composite video burst signal X_(CVBS) isoutput.

In operation 908, the decoder prediction unit 734 filters and decodesthe predicted value X′_(CVBS) of the composite video burst signalX_(CVBS), by applying a different YC separation filter, and outputs apredicted value, {tilde over (x)}, of the input video signal.

In the current exemplary embodiment, the artifact detection and removalunit 730 is connected to a back end of the system decoder unit 720, butit can also be connected to a front end of the system encoder unit 710so that artifacts can be removed through the process described above.

FIG. 10 is a block diagram illustrating a structure of an apparatus fordetecting and removing artifacts according to another exemplaryembodiment of the present invention. Referring to FIG. 10, the apparatusfor detecting and removing artifacts is composed of an artifactdetection unit 1010 and an artifact removal unit 1020. For convenienceof explanation, the system encoder 710 and the system decoder 720 ofFIG. 2 are also illustrated. Also, the apparatus for detecting andremoving artifacts of the current exemplary embodiment can be applied tothe artifact detection and removal unit 330 of FIG. 3.

The artifact detection unit 1010 is composed of an RGB-YIQ color spacetransform unit (E₁) 1012, a color modulation unit E₂) and YC additionunit (E₃) 1014, and an artifact detection map generation unit 1016.

The RGB-YIQ color space transform unit (E₁) 1012 transforms the outputvideo signal X′ into X′_(YIQ) formed with a luminance signal, anin-phase signal and an orthogonal signal.

The color modulation unit (E₂) and YC addition unit (E₃) 1014synthesizes the in-phase signal and the orthogonal-phase signal into achrominance signal, and synthesizes the chrominance signal and theluminance signal into a composite video burst signal X′_(CBS),respectively.

The artifact detection map generation unit 1016 detects artifacts bycomparing the luminance signals of X′_(YIQ) and X′_(CVBS), and generatesan artifact detection map X′_(MAP) using equation 25 below:

$\begin{matrix}{\left( x_{MAP}^{\prime} \right)_{k} = \left\{ {\begin{matrix}{1,} & {{{\left( {L\left( x_{CVBS}^{\prime} \right)} \right)_{k} - \left( x_{Y}^{\prime} \right)_{k}}} > {Th}_{MAP}} \\{0,} & {otherwise}\end{matrix},{k = 0},1,\ldots\mspace{11mu},{{MN} - 1}} \right.} & (25)\end{matrix}$where L(.) is a low pass filter, and a 1 MHz 9-tap low pass filter isused. Also, x′_(y)=[Y′₀ Y′₁ . . . Y′_(MN-1)] is a vector formed withonly Y components in X′_(YIQ) and Th_(MAP) is a threshold for detectingartifacts.

However, the cutoff frequency and the number of taps are not limited to1 MHz and 9 taps, and other values can be applied selectively in otherembodiments.

The artifact removal unit (D₃D₂D₁) 1020 is composed of a YC separationunit (D₃), a color demodulation unit (D₂) and a YIQ-RGB color spacetransform unit (D₁).

The artifact removal unit (D₃D₂D₁) 1020 filters and decodes an artifactdetection area according to an artifact detection map and outputs asignal {tilde over (x)} from which artifacts have been removed.

Thus, if filtering is performed only for the artifact detection area, itgives an advantage that artifacts occurring in a decoding process do notoccur in an area where no artifacts occurred.

The YC separation filter uses a filter different from the YC separationfilter used in a system decoder. A vector {circumflex over (d)}₃ formingthe YC separation filter (D3) in a decoder prediction unit is defined inequation 26 below:

$\begin{matrix}{\left( {\hat{d}}_{3} \right)_{k} = \left\{ {\begin{matrix}{\left( {\hat{d}}_{3,1} \right)_{k},} & {{{if}\mspace{14mu}\left( x_{MAP}^{\prime} \right)_{k}} = 1} \\{\left( {\hat{d}}_{3,2} \right)_{k},} & {otherwise}\end{matrix},{k = 0},1,\ldots\mspace{11mu},{{MN} - 1}} \right.} & (26)\end{matrix}$where {circumflex over (d)}_(3,l) (l=1,2) is defined in equation 27below:

$\begin{matrix}{{\left( {\hat{d}}_{3,l} \right)_{k} = \frac{\left( x_{Y}^{\prime} \right)_{k}}{\left( x_{CVBS}^{\prime} \right)_{k}}},{k = 0},1,\ldots\mspace{11mu},{{MN} - 1},{l = 1},2} & (27)\end{matrix}$

In the case of {circumflex over (d)}_(3,l), X′_(Y) is Y obtained using a2H comb filter in the decoder prediction unit of FIG. 7.

FIG. 11 is a flowchart illustrating a method of detecting and removingartifacts according to another exemplary embodiment of the presentinvention.

A process of inputting the input video signal X and outputting theoutput video signal X′ in FIG. 11 is the similar to operations 902 and904, and thus, an explanation will be omitted here.

In operation 1102, the output video signal X′ is transformed into aluminance signal, an in-phase signal and an orthogonal-phase signal.

In operation 1104, the in-phase signal and the orthogonal-phase signalare synthesized into a chrominance signal and the chrominance signal andthe luminance signal are synthesized into composite video burst signalX′_(CVBS).

In operation 1106, the luminance signal and a signal obtained byfiltering the composite video burst signal X′_(CVBS) are compared and anartifact detection map is generated.

In operation 1108, artifacts are removed by filtering the artifactdetection area according to the artifact detection map.

Though the artifact detection unit 1010 and the artifact removal unit1020 are connected to the back end of the system decoder unit 720 in thecurrent exemplary embodiment, they can be connected to the front end ofthe system decoder unit 720 so that artifacts can be removed through theprocess described above.

FIG. 12 is a block diagram illustrating a structure of an apparatus fordetecting and removing artifacts according to still another exemplaryembodiment of the present invention. In the current exemplaryembodiment, unlike the exemplary embodiments of FIGS. 7 and 10, it isdetermined whether an area where an artifact occurs is a motion area andthe type of artifact that occurs. Then, according to the determinationresult, a time filter and a space filter are applied appropriately tothe determination result so that the artifact can be removed.

Referring to FIG. 12, the apparatus for detecting and removing artifactsaccording to the current exemplary embodiment is composed of a motionarea detection unit 1202, an artifact detection unit 1210, a motioncompensation unit 1220, a time filter 1232, a space filter 1234, and amultiplexing unit 1240.

If an output video signal is input, the motion area detection unit 1202generates a motion detection map M_(map) and a motion compensation mapMC_(map) by using motion information between two neighboring frames inthe output video signal.

The artifact detection unit 1210 is composed of a rainbow effectdetection unit 1212 and a dot crawl artifact detection unit 1214.

The rainbow effect detection unit 1212 detects a rainbow effect andgenerates a rainbow effect detection map, RB_(map). The rainbow effectis an artifact in which when an image moves fast, a luminance signalremains in a chrominance signal and thus rainbow colors are seen in anarea where a big difference of brightness occurs.

The dot crawl artifact detection unit 1214 detects a dot crawl artifactand generates a dot crawl artifact detection map, DC_(map). The dotcrawl artifact is an artifact in which a chrominance signal remains in aluminance signal and thus a dot crawl occurs.

The motion compensation unit 1220 compensates for a motion when an areahaving an artifact is moved, so that the artifact can be removed throughtime filtering.

The time filter 1232 removes artifacts in an area where no motionexists. Also, in the case of an area where motion exists, if the motioncompensation unit 1220 compensates for motion according to a motioncompensation map MC_(map), the time filter 1232 filters the motioncompensated image and thus removes the artifact.

When dot crawl artifact detection maps of two frames do not match, thespace filter 1234 is used to remove the artifacts.

According to control signals of the motion detection map M_(map), andthe motion compensation map MC_(map) in relation to an area in whichartifacts occur, and a dot crawl artifact detection map DC_(map)^((x,y,t)) in a current frame, a dot crawl artifact detection mapDC_(map) ^((x,y,t-1)) in the previous frame, and a rainbow effectdetection map RB_(map), the multiplexing unit 1240 performs filtering bycombining the time filter 1232 and the space filter 1234 so that anartifact-free signal can be output.

FIG. 13 is a flowchart illustrating a method of detecting and removingartifacts according to still another exemplary embodiment of the presentinvention.

In operation 1302, if a output video signal is input, estimate a motionvector from two neighboring frames in output video signal and generate amotion detection map M_(map), a motion compensation map MC_(map) basedon the motion vector In operation 1304, a dot crawl artifact is detectedand a dot crawl artifact detection map DC_(map) is generated. Also, arainbow effect is detected and a rainbow effect detection map RB_(map)is generated.

In operation 1306, according to control signals of the motion detectionmap M_(map), and the motion compensation map MC_(map) in relation to anarea in which artifacts occur, and a dot crawl artifact detection mapDC_(map) ^((x,y,t)) in a current frame, a dot crawl artifact detectionmap DC_(map) ^((x,y,t-1)) in the previous frame, and a rainbow effectdetection map RB_(map), by combining a time filter and a space filter,filtering is performed and an artifact-free signal is output.

FIG. 14 is a diagram illustrating an operation used to detect a motionaccording to an exemplary embodiment of the present invention.

The motion area detection unit 1202 extracts motion information betweentwo neighboring frames and divides the information into a motion areaand a motionless area.

In order to use motion information, the motion area detection unit 1202uses a block matching algorithm (BMA). The block matching algorithmestimates a motion, by using the bright value difference between acurrent frame block and the previous frame block. In the block matchingmethod, the brightness values of blocks of each of a plurality ofcontinuous frames are compared with the brightness value of the previousframe in order to estimate a motion vector. In the block matchingalgorithm, the current frame is divided into blocks, each having a smallM×N size without overlapping between the blocks, and the brightnessvalue in each block is compared. In a search range, an area having asmallest value of a mean absolute difference (MAD) or a mean squaredifference (MSD) value is searched for with respect to the position ofeach block in the current frame 1404. The position of the previous imagethus found and a position displacement of the current image are definedas motion vectors.

In FIG. 14, the diagram 1402 on the left-hand side is the previous frameand the diagram 1404 on the right-hand side is the current frame. FIG.14 illustrates that an in-phase signal and an orthogonal-phase signalremain in a luminance signal because YC separation is not performedcorrectly. Since the characteristic of a composite video burst signal isreflected in the output image of a decoder in the NTSC system, pixels ofthe decoded image are classified into 4 types, Y+ΔI, Y−ΔI, Y+ΔQ, Y−ΔQ,with respect to an in-phase signal and an orthogonal-phase signal.

Each of the in-phase signal and the orthogonal-phase signal has acharacteristic that the signal is positioned at every second pixel, andin two contiguous frames, the phase of the signal is reversed. By usingthis characteristic, the motion area detection unit 1202 detects motion.Also, when filtering a signal by compensating for motion, a block isfound using this characteristic. Then, by using the found block and atime filter, dot crawl artifacts and rainbow effects are removed.

In a search range of the block matching algorithm, while moving in unitsof 2 pixels in the X axis direction and 1 pixel in the Y axis direction,a block having a smallest displaced frame difference (DFD) is found todetermine a motion vector. The DFD is defined in equation 28 below:d(x,y;t)=F _(y)(x,y;t)−F _(y)(x−u,y−v;t−1)  (28)where x is an abscissa, y is an ordinate in the image, and u and v arevalues indicating amounts moved in the X direction and in the Ydirection, respectively. Here, the motion vector is defined in equation29 below:

$\begin{matrix}{\left( {{u\left( {x,y,t} \right)},{v\left( {x,y,t} \right)}} \right) = {\underset{{({u^{\prime},v})} \in S}{\arg\mspace{11mu}\min}{\quad\left\{ {\sum\limits_{i = {{- {bs}}/2}}^{{{bs}/2} - 1}\;{\sum\limits_{j = {{- {bs}}/2}}^{{{bs}/2} - 1}\;\left. {{F_{Y}\left( {{x + i},{{y + j};t}} \right)} - {F_{Y}{\quad\left( {{x + i - u^{\prime}},{{y + j - v^{\prime}};{t - 1}}} \right)}}} \right\}}} \right.}}} & (29)\end{matrix}$where bs is an even number and is a size of a block, and (i, j) arecoordinates in the block and are found in the search range S. In thecurrent exemplary embodiment, whether a motion exists is determinedbased on a motion vector. By determining whether motion exists, a motiondetection map M_(map) defined in equation 30 below can be generated:

$\begin{matrix}{{M_{map}\left( {x,{y;t}} \right)} = \left\{ \begin{matrix}{1,} & {\left( {{u\left( {x,y,t} \right)},{v\left( {x,{y;t}} \right)}} \right) > T_{m}} \\{0,} & {otherwise}\end{matrix} \right.} & (30)\end{matrix}$where T_(m) is a motion threshold, M_(map)=0 indicates a motionless areaand M_(map)=1 is an area containing motion. Artifacts can occur both ina motion area and a motionless area. In these cases, filters suitablefor respective areas are selected and the artifacts are removed. Theeffect of noise is reduced when a motion is searched according to theblock matching algorithm compared to when a motion is searched in unitsof pixels.

A motion compensation map MC_(map), which is another element formingmotion information in addition to the motion detection map M_(map), isdefined in equation 31 below:

$\begin{matrix}{{{MC}_{map}\left( {x,{y;t}} \right)} = \left\{ \begin{matrix}{1,} & {{d\left( {x,{y;t}} \right)} < T_{mc}} \\{0,} & {otherwise}\end{matrix} \right.} & (31)\end{matrix}$where T_(mc) is a motion compensation filter threshold. When MC_(map)=1,a motion compensation filter is used and when MC_(map)=0, a motioncompensation filter is not used.

FIG. 15 is a diagram illustrating a method of detecting a dot crawlartifact according to an exemplary embodiment of the present invention.

FIG. 15 illustrates a case where dot crawl artifacts occur in thevicinity of a horizontal color outline. The diagram 1502 on theleft-hand side is a composite video burst signal that is a signal beforedecoding is performed. The composite video burst signal comprises aluminance signal, an in-phase signal and an orthogonal-phase signal. Thediagram 1504 on the right-hand side is a luminance signal expressed incolors obtained by performing operations between neighboring lines in a1H comb filter. After decoding, the signal is divided into a luminancesignal, an in-phase signal, and an orthogonal signal, and the dividedsignals are output to frames, respectively. A dot crawl artifact occurswith each four pixels being one period, as illustrated in the right-handdiagram 1504, and the value of the dot crawl artifact is expressed inequation 32 below:2Y+(I−I′)2Y+(Q−Q′), 2Y+(−I+I′), 2Y+(−Q+Q′)  (32)where I and I′ and Q and Q′ indicate that the values of anorthogonal-phase signal and an in-phase signal between neighboringpixels are different. When I=I′ or Q=Q′, the output of a comb filteronly has a Y component and thus a dot crawl artifact does not occur.However, if a color outline exists, a color component remains.

The color component remaining in the decoded luminance signal isexpressed in equation 33 below:|I−I′|=|−I+I′||Q−Q′|=|−Q+Q′|  (33)

The absolute values are the same as in equation 33 or the difference ofthe absolute values is small. By considering the characteristic of thedot crawl artifact, a dot crawl artifact detection map DC_(map) isgenerated.

Two image frames having artifacts are input and a dot crawl pattern issearched for at a position where M_(map)=1 in a motion detection mapM_(map) generated previously by the motion area detection unit 1202. Thedot crawl pattern is determined with respect to each of the two framescontinuously input according to equation 34 below:

$\begin{matrix}{{{DC}_{map}\left( {x,{y;t}} \right)} = \left\{ \begin{matrix}{1,} & \begin{matrix}{{{{{Y\left( {x,{y;t}} \right)} - {Y\left( {{x + 2},{y;t}} \right)}}} - {{{Y\left( {{x + 2},{y;t}} \right)} - {Y\left( {{x + 4},{y;t}} \right)}}}} < {T_{dc}\mspace{14mu}{and}}} \\{{{{{Y\left( {{x + 1},{y;t}} \right)} - {Y\left( {{x + 3},{y;t}} \right)}}} - {{{Y\left( {{x + 3},{y;t}} \right)} - {Y\left( {{x + 5},{y;t}} \right)}}}} < {T_{dc}\mspace{14mu}{and}}} \\{{Y\left( {x,{y;t}} \right)} \neq {Y\left( {x,{{y - 1};t}} \right)} \neq {Y\left( {x,{{y + 1};t}} \right)}}\end{matrix} \\{0,} & {otherwise}\end{matrix} \right.} & (34)\end{matrix}$where T_(dc) is a threshold suitable to detect a dot crawl artifact,DC_(map)(x,y,t) is a dot crawl artifact detection map in the currentframe and DC_(map)(x,y,t−1) is a dot crawl artifact detection map in theprevious frame.

The reason why detection of a dot crawl pattern is performed withrespect to each frame is to efficiently remove dot crawl artifactsthrough an appropriate filter and to reduce a danger of occurrence ofnew artifacts.

FIG. 16 is a diagram illustrating a method of detecting a rainbow effectaccording to an exemplary embodiment of the present invention. Thediagram 1602 on the left-hand side is a case where a rainbow effect doesnot occur and the diagram 1604 on the right-hand side is a case where arainbow effect occurs. That is, unlike the diagram 1602 on the left-handside, in the diagram 1604 on the right-hand side it can be seen that aluminance signal is mixed with an in-phase signal and anorthogonal-phase signal. In this case, a rainbow effect occurs. In orderto detect this rainbow effect, by using the characteristic of acomposite video burst signal that the values of color components in twoneighboring frames are different from each other, an area in which thevalue of equation 35 below is in a threshold range is searched for:d _(I) =|F _(I)(x,y;t)−F _(I)(x,y;t−1)|d _(Q) =|F _(Q)(x,y;t)−F _(Q)(x,y;t−1)|  (35)

If an area where a rainbow effect occurs is found according to thedetection method, pixels in which the rainbow effect occurs are foundaccording to equation 36 below:

$\begin{matrix}{{{RB}_{map}\left( {x,{y;t}} \right)} = \left\{ \begin{matrix}{1,} & \begin{matrix}{{{F_{Y}\left( {x,{y;t}} \right)} > {T_{Y}\mspace{14mu}{and}\mspace{14mu}{M_{map}\left( {x,{y;t}} \right)}}} = 1} \\{\left( {\left( {T_{I\; 1} < {{{F_{I}\left( {x,{y;{t - 1}}} \right)} - {F_{I}\left( {x,{y;t}} \right)}}} < T_{I\; 2}} \right)\mspace{14mu}{or}} \right.} \\\left. \left( {T_{Q\; 1} < {{{F_{Q}\left( {x,{y;{t - 1}}} \right)} - {F_{Q}\left( {x,{y;t}} \right)}}} < T_{Q\; 2}} \right) \right)\end{matrix} \\{0,} & {otherwise}\end{matrix} \right.} & (36)\end{matrix}$

FIG. 17 is a diagram illustrating the time filter 1232 of FIG. 12according to an exemplary embodiment of the present invention. FIG. 17illustrates dot crawl patterns in neighboring frames, and a compositevideo burst signal has a characteristic that the phases of color signalsin neighboring frames are opposite to each other. Referring to FIG. 17,the dot crawl patterns of the previous frame 1701 and the current frame1702 show one pixel difference in the positions of the bright and darkdots. By using this characteristic, when no motion exists, simple timefiltering is used, so that artifacts such as a dot crawl artifact and arainbow effect can be removed through time filtering according toequation 37 below:

$\begin{matrix}{{\hat{F}\left( {x,{y;t}} \right)}_{stationary} = \frac{{F\left( {x,{y;t}} \right)} + {F\left( {x,{y;{t - 1}}} \right)}}{2}} & (37)\end{matrix}$where {circumflex over (F)}(x,y;t)_(stationary) is a value filtered in amotionless area where no motion exists. In an area where a motionexists, a simple time filter cannot be used. However, when thecharacteristic of the NTSC artifacts is considered, a time filter can beused effectively, though in a limited scope. For example, if dot crawlartifact detection maps of the previous frame and the current frame areat identical positions, the dot crawl artifact can be removed through asimple time filtering method.

A dot crawl pattern and a rainbow effect occurring in an area where amotion exists cannot be removed through a simple time filter. In thecase of the dot crawl pattern, due to the phase inverting characteristicof a composite video burst signal, the dot crawl pattern appears toblink in continuous frames. If in neighboring frames in which a rainboweffect occurs, the brightness values do not change and only movement ofa position occurs between the frames, the rainbow effect can be removedthrough a time filter by compensating for a motion. When the motion iscompensated for, the dot crawl artifact and rainbow effect are removedthrough a time filter according to equation 38 below:

$\begin{matrix}{{\hat{F}\left( {x,{y;t}} \right)}_{MC} = \frac{{F\left( {x,{y;t}} \right)} + {F\left( {{x - u},{{y - v};{t - 1}}} \right)}}{2}} & (38)\end{matrix}$where {circumflex over (F)}(x,y;t)_(MC) is the brightness value of aframe which is time filtered for motion compensation, (x,y) is theposition in the frame, and (x−u, y−v) is the motion-compensatedposition.

FIG. 18 is a diagram illustrating the space filter 1234 of FIG. 12according to an exemplary embodiment of the present invention. FIG. 18illustrates a neural network weight calculator for removing a dot crawlartifact. A space filter in the current exemplary embodiment removes adot crawl artifact in units of pixels by using a neural network circuit.The weight (weighting coefficient) of a neural network circuit isobtained through training. If an input video signal passes through thesystem encoder 710 and the system decoder 720 of FIG. 7, it becomes asignal in which artifacts occur in the process of modulation anddemodulation. The distorted image signal is divided through an areaseparator 1802 and the divided signals are input to respective neuralnetwork circuits.

The neural network circuits 1 and 2, 1812 and 1814, extract brightnessvalues corresponding to an M×N size mask from a pixel in which anartifact is detected, extract brightness values at the same position inthe original image, set the values as the input value and the targetvalue, respectively, of the neural network circuits, and performtraining.

In the current exemplary embodiment, a back propagation algorithm 1816is used for training of a neural network circuit. According to the backpropagation algorithm 1816, the weight of a neural network circuit isdetermined so that the difference of input values and target values,that is, errors, can be minimized.

Since neural network circuits 1 and 2 are trained using different typesof training data, neural network circuits 1 and 2 have weights that aredifferent from each other. Neural network circuit 1 has inputs of a dotcrawl pattern in an area where motion exists and brightness values ofadjacent pixels, and has a target value of the brightness value of apixel at the same position in the original image. Training data ofneural network circuit 2 has inputs of a dot crawl pattern in an areawhere no motion exists and brightness values of adjacent pixels, and hasa target value of the brightness value of a pixel at the same positionin the original image.

A neural network circuit is composed of an input layer having L nodes, ahidden layer having M nodes, and an output layer having N nodes. Asinputs of each direction of a neural network circuit, pixels in a maskincluding L pixels centered at a pixel in which an artifact is detected,are extracted from an image, I_(f)(m,n), in which an artifact exists atthe same position that pixels are detected in, and used. As a targetvalue, a value of a pixel centered in a mask is extracted from the sameposition which the pixel is located in the input video signal I(m,n) andused.

The neural network circuit applies a weight suitable for the pixel at aposition in which an artifact is detected by using a weight valueobtained through training and direction information of the artifact, andremoves artifacts in units of pixels. In a pixel-unit artifact removalblock using the weight of the neural network circuit, outputI′_(f)(m,n), is calculated according to equation 39 below:

$\begin{matrix}{{I_{f}^{\prime}\left( {m,n} \right)} = \left\{ \begin{matrix}{{{\sum\limits_{i = 1}^{M}\;{c_{i}^{1}{w_{i,1}^{2}(k)}}} + b_{i}^{2}},} & {{{if}\mspace{14mu}{B_{f}\left( {x,y} \right)}} = 1} \\{{I_{f}\left( {m,n} \right)},} & {otherwise}\end{matrix} \right.} & (39)\end{matrix}$where I_(f)(m,n) is an image in which artifacts exist, and B_(f)(x,y) isa position where an artifact exists, and if B_(f)(x,y)=1, the pixel is apixel in which an artifact is detected.

Also, intermediate process calculated value C_(i) ¹ in the neuralnetwork circuit is calculated according to equation 40 below:

$\begin{matrix}{c_{i}^{1} = {{\sum\limits_{j = 1}^{L}{p_{j}{w_{j,i}^{1}(k)}}} + b_{i}^{1}}} & (40)\end{matrix}$where the superscript of w¹ _(j,i)(k), which indicates a weight, is theposition of a layer; subscripts i and j indicate positions of nodes,respectively, at two continuous layers; and b_(t) ¹ is a bias in whichthe superscript and subscript indicate the positions of the layer andthe node, respectively.

The dot crawl artifacts and adjacent pixel values passing through eachneural network circuit are output as weighted values close to the valuesin the original image. By training neural network circuits with avariety of images, and a variety of patterns of dot crawl artifacts, theneural network circuits are made to operate as filters adaptive toimages of a variety of environments.

In another exemplary embodiment, when dot crawl detection maps of twoframes do not match, a space filter can perform space filtering of thebrightness value of one period according to equation 41 below, by usingthe characteristic that an artifact has a pattern repeating with aperiod of 4 pixels:

$\begin{matrix}{{\hat{F}\left( {x,{y;t}} \right)}_{spatial} = \frac{\begin{matrix}{{F\left( {{x - 1},{y;t}} \right)} + {F\left( {{x + 1},{y;t}} \right)} +} \\{{F\left( {x,{{y - 1};t}} \right)} + {F\left( {x,{{y + 1};t}} \right)}}\end{matrix}}{4}} & (41)\end{matrix}$where {circumflex over (F)}(x, y; t)_(spatial) is a brightness valueobtained by space filtering a dot crawl artifact.

FIG. 19 is a diagram illustrating the multiplexing unit 1240 of FIG. 12according to an exemplary embodiment of the present invention.

The multiplexing unit 1240 performs filtering by combining the timefilter 1232 and the space filter 1234, using two neighboring frames asinputs and with reference to the control signals of a motion detectionmap M_(map), and a motion compensation map MC_(map), a dot crawlartifact detection map DC_(map) ^((x,y,t)) in the current frame, a dotcrawl artifact detection map DC_(map) ^((x,y,t-1)) in the previousframe, and a rainbow effect detection map RB_(map). The filter providedby the multiplexing unit 1240 is expressed as equation 42 below:

$\begin{matrix}{{\hat{F}\left( {x,{y;t}} \right)} = \left\{ \begin{matrix}{\frac{{F\left( {x,{y;t}} \right)} + {F\left( {x,{y;{t - 1}}} \right)}}{2},} & {{M_{map}\left( {x,{y;t}} \right)} = 0} \\{\frac{{F\left( {x,{y;t}} \right)} + {F\left( {{x - u},{{y - v};{t - 1}}} \right)}}{2},} & \begin{matrix}{{M_{map}\left( {x,{y;t}} \right)} = {{1\mspace{14mu}{and}\mspace{14mu}{{MC}_{map}\left( {x,{y;t}} \right)}} = 1}} \\{\left( {\left( {{{DC}_{map}\left( {x,{y;t}} \right)} = {{1\mspace{14mu}{and}\mspace{14mu}{{DC}_{map}\left( {x,{y;{t - 1}}} \right)}} = 1}} \right)\mspace{14mu}{or}} \right.} \\\left. {{{and}\mspace{14mu}{{RB}_{map}\left( {x,{y;t}} \right)}} = 1} \right)\end{matrix} \\\frac{\begin{matrix}{{F\left( {{x - 1},{y;t}} \right)} + {F\left( {{x + 1},{y;t}} \right)} +} \\{{F\left( {x,{{y - 1};t}} \right)} + {F\left( {x,{{y + 1};t}} \right)}}\end{matrix}}{4} & \begin{matrix}{{M_{map}\left( {x,{y;t}} \right)} = {1\mspace{14mu}{and}}} \\\left( {\left( {{{DC}_{map}\left( {x,{y;{t - 1}}} \right)} = {{1\mspace{14mu}{and}\mspace{14mu}{{DC}_{map}\left( {x,{y;t}} \right)}} = 0}} \right)\mspace{14mu}{or}} \right. \\\left. \left. {{{DC}_{map}\left( {x,{y;{t - 1}}} \right)} = {{0\mspace{14mu}{and}\mspace{14mu}{{DC}_{map}\left( {x,{y;t}} \right)}} = 1}} \right) \right)\end{matrix} \\{{F\left( {x,{y;t}} \right)},} & {otherwise}\end{matrix} \right.} & (42)\end{matrix}$where {circumflex over (F)}(x,y;t) is an output value in which theartifact is removed through the filter.

FIG. 20 is a table illustrating the relations between control signals ofthe multiplexing unit and filters according to an exemplary embodimentof the present invention. Referring to FIG. 20, for example, in the caseof the top line, the top line indicates that the area is a motionlessarea and thus no motion exists and M_(map)=0. Maps related to otherartifacts are not required and in this case, a time filter is applied.In this way, a time filter or a space filter is applied according torespective control signals.

The systems to which the present invention is applied are not limited tothe NTSC system and can also include a phase-alternating line (PAL)system and a Séquentiel couleur á mémoire (SECAM) system.

The present invention can also be embodied as computer readable codes ona computer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include, but are not limited to, read-only memory(ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppydisks, and optical data storage devices. The computer readable recordingmedium can also be distributed over network coupled computer systems sothat the computer readable code is stored and executed in a distributedfashion.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims. Theexemplary embodiments should be considered in descriptive sense only andnot for purposes of limitation. Therefore, the scope of the invention isdefined not by the detailed description of the invention but by theappended claims, and all differences within the scope will be construedas being included in the present invention.

According to the exemplary embodiment of the present invention asdescribed above, filtering is performed before a decoding operation, andthrough the preprocessing process noise in relation to a 1D signal isremoved. Then, by using a variety of methods of detecting and removingartefacts, artefacts are removed so that the picture quality of acomposite video burst signal can be improved.

1. A method of improving picture quality in a composite video burstsignal, the method comprising: dividing the composite video burst signalinto a plurality of frequency bands using a low pass filter and a highpass filter; performing wavelet packet filtering of a frequency bandincluding a chrominance signal having energy higher than a firstthreshold, among the plurality of frequency bands; and performing Wienerfiltering of a frequency band including a chrominance signal havingenergy lower than a second threshold, among the plurality of frequencybands.
 2. The method of claim 1, wherein the performing of the waveletpacket filtering comprises: dividing the composite video burst signalinto a further plurality of frequency bands; generating wavelettransform coefficients by applying wavelet transforms to signals in thefurther plurality of frequency band; and removing a signal in afrequency band having a generated wavelet transform coefficient whoseabsolute value is less than a specified threshold.
 3. The method ofclaim 1, wherein in the performing Wiener filtering, a size of a mask isvaried with respect to a magnitude of a noise ratio.
 4. The method ofclaim 1, further comprising: separating the divided composite videoburst signal into a luminance signal and a chrominance signal;separating the chrominance signal into an in-phase signal and anorthogonal-phase signal; and transforming the luminance signal, thein-phase signal and the orthogonal-phase signal into a red (R) signal, agreen (G) signal, and a blue (B) signal, respectively; and outputting anoutput video signal.
 5. The method of claim 4, further comprisingdetecting and removing an artifact of the output video signal, whereinthe detecting and removing of the artifact comprises: encoding theoutput video signal and outputting a predicted value of a compositevideo burst signal; and filtering the output predicted value of thecomposite video burst signal by using a luminance/chrominance (YC)separation filter of a type different from that of a YC separationfilter for separating a luminance signal and a chrominance signal in asystem decoder.
 6. The method of claim 4, further comprising detectingand removing an artifact of the output video signal, wherein thedetecting and removing the artifact comprises: transforming the outputvideo signal into a luminance signal, an in-phase signal and anorthogonal-phase signal; synthesizing the in-phase signal and theorthogonal signal into a chrominance signal; synthesizing the luminancesignal and the chrominance signal into a composite video burst signal;generating an artifact detection map indicating an area where anartifact occurs, by comparing the luminance signal and a signal obtainedby low pass filtering the composite video burst signal; and filteringthe area where the artifact is detected according to the artifactdetection map, by using a YC separation filter of a type different fromthat of a YC separation filter for separating a luminance signal and achrominance signal in a system decoder.
 7. The method of claim 4,further comprising detecting and removing an artifact of the outputvideo signal, wherein the detecting and removing the artifact comprises:estimating a motion vector from two neighboring frames in the outputvideo signal; generating a motion detection map indicating whethermotion exists between two neighboring frames and a motion compensationmap indicating whether a motion compensation filter is used based on themotion vector; detecting a dot crawl artifact occurring in the vicinityof an outline of an image and generating a dot crawl artifact detectionmap, or detecting a rainbow effect in which rainbow colors are seen inan area where a difference of brightness occurs when an image movesfast, and generating a rainbow effect detection map; compensating for amotion according to the motion compensation map; and filtering an areawhere the artifact occurs by combining a time filter and a space filterbased on control signals of the motion detection map, the motioncompensation map, the dot crawl artifact detection map in a currentframe, the dot crawl artifact detection map in a previous frame, and therainbow effect detection map.
 8. An apparatus for improving picturequality in a composite video burst signal, the apparatus comprising: apreprocessing filter which filters the composite video burst signal byusing a wavelet packet filter and a Wiener filter; aluminance/chrominance (YC) separation unit which separates the filteredcomposite video burst signal into a luminance signal and a chrominancesignal; a color demodulation unit which separates the chrominance signalinto an in-phase signal and an orthogonal-phase signal; and a YIQ-RGBcolor space transform unit which transforms the luminance signal,in-phase signal and orthogonal-phase signal into a red (R) signal, agreen (G) signal, and a blue (B) signal, respectively, and outputs anoutput video signal.
 9. The apparatus of claim 8, further comprising anartifact detection and removal unit which detects and removes anartifact of the output video signal, wherein the artifact detection andremoval unit comprises: an encoder prediction unit which encodes theoutput video signal and outputs a predicted value of a composite videoburst signal; and a decoder prediction unit which decodes the outputpredicted value of the composite video burst signal and outputs apredicted value of an input video signal.
 10. The apparatus of claim 9,wherein the decoder prediction unit comprises: a luminance/chrominance(YC) separation unit which performs filtering to separate the predictedvalue of the composite video burst signal into an in-phase signal and anorthogonal-phase signal, using a YC separation filter of a typedifferent from that of a YC separation filter for separating a luminancesignal and a chrominance signal in a system decoder; a colordemodulation unit which separates the chrominance signal into anin-phase signal and an orthogonal-phase signal; and a YIQ-RGB colorspace transform unit which transforms the luminance signal, the in-phasesignal and the orthogonal-phase signal into an R signal, a G signal, anda B signal, respectively, as a predicted value of the input videosignal.
 11. The apparatus of claim 8, further comprising an artifactdetection and removal unit which detects and removes an artifact of theoutput video signal, wherein the artifact detection and removal unitcomprises: an RGB-YIQ color space transform unit which transforms theoutput video signal into a luminance signal, an in-phase signal and anorthogonal-phase signal; a color modulation unit which synthesizes thein-phase signal and the orthogonal signal into a chrominance signal; aluminance/chrominance (YC) addition unit which synthesizes the luminancesignal and the chrominance signal into a composite video burst signal;an artifact detection map generation unit which generates an artifactdetection map indicating an area where an artifact occurs by comparingthe luminance signal and a signal obtained by low pass filtering thecomposite video burst signal; and an artifact removal unit which removesartifacts by decoding the composite video burst signal according to theartifact detection map.
 12. The apparatus of claim 11, wherein theartifact removal unit comprises: a luminance/chrominance (YC) separationunit which performs filtering to separate the area where the artifact isdetected according to the artifact detection map into a luminance signaland a chrominance signal using a YC separation filter of a typedifferent from that of a YC separation filter for separating a luminancesignal and a chrominance signal in a system decoder; a colordemodulation unit which separates the chrominance signal into anin-phase signal and an orthogonal-phase signal; and a YIQ-RGB colorspace transform unit which transforms the luminance signal, the in-phasesignal and the orthogonal-phase signal into an R signal, a G signal, anda B signal, respectively, and outputs an artifact-free signal.
 13. Theapparatus of claim 8, further comprising an artifact detection andremoval unit which detects and removes an artifact of the output videosignal, wherein the artifact detection and removal unit comprises: amotion area detection unit which estimates a motion vector from twoneighboring frames in the output video signal, generates a motiondetection map indicating whether motion exists between two neighboringframes and a motion compensation map indicating whether a motioncompensation filter is used based on the motion vector; an artifactdetection unit which generates a dot crawl artifact detection map bydetecting a dot crawl artifact occurring in the vicinity of an outlineof an image, or generating a rainbow effect detection map by detecting arainbow effect in which rainbow colors are seen in an area where adifference of brightness occurs when an image moves fast; a motioncompensation unit which compensates for a motion according to the motioncompensation map; and a multiplexing unit which filters an area wherethe artifact occurs, by combining a time filter and a space filter basedon control signals of the motion detection map, the motion compensationmap, the dot crawl artifact detection map in a current frame, the dotcrawl artifact detection map in a previous frame, and the rainbow effectdetection map.
 14. A non-transitory computer readable recording mediumhaving embodied thereon a computer program for executing the method ofimproving picture quality in a composite video burst signal of claim 1.15. A non-transitory computer readable recording medium having embodiedthereon a computer program for executing the method of improving picturequality in a composite video burst signal of claim 7.